1. Surface of the Invention
The present invention relates to an objective lens drive apparatus provided to focus a light beam from an objective lens onto an optical disk as a light spot in order to perform recording/reproduction of the optical disk, and relates to an optical pickup device incorporating the objective lens drive apparatus, and an optical disk drive incorporating the optical pickup device.
2. Description of the Related Art
Conventionally, in the optical disk drive, the laser light beam, output from the laser light source, is focused with the objective lens on the optical disk as a light spot, and information is read from the optical disk by carrying out the opto-electric conversion of the reflected light from the optical disk.
The objective lens drive apparatus, which is provided in the optical disk drive, drives the objective lens in the focusing direction and the tracking direction using the control signal obtained from the reflected light, and causes the proper light spot to be formed on the recording surface of the optical disk by controlling the movement of the objective lens to follow the motion of the surface inclination of the optical disk or the eccentricity thereof.
In recent years, with the trend of high-density information recording, there is the demand to form the small light spot on the optical disk. To realize this, it is necessary to enlarge the NA (numerical aperture) of the objective lens or to shorten the wavelength of laser.
However, if the NA is enlarged or the wavelength of laser is shortened, the perpendicularity of the optical axis of the objective lens to the optical disk is shifted, and the coma aberration will easily be generated and the quality of the light spot will deteriorate. This causes the quality of recording/reproduction to deteriorate.
In order to attain high-density information recording, it is necessary to raise the inclination accuracy between the optical disk and the objective lens.
On the other hand, when processing mass data with the trend of high-density information recording, the improvement of the speed of recording/reproduction is desired, and it is necessary to carry out high-speed rotation of the optical disk.
When the high-speed rotation of the optical disk with which the surface inclination or the eccentricity exists is carried out, the accelaration becomes very large. In order to make the objective lens follow the optical disk with sufficient accuracy, the objective lens drive apparatus that is capable of generating a large force is needed.
There are some conceivable methods to correct the inclination between the optical disk and the objective lens. One of such methods is to make the movable portion of the objective lens drive apparatus containing the optical disk follow the inclination of the optical disk. This method will provide the high-speed capability to follow the rotational speed of the optical disk, with low cost.
For example, in the case of the method, consideration is given to incline the movable portion of the objective lens drive apparatus in the radial direction and the tangential direction. To realize this, the mechanism to drive the movable portion in the four axial directions, including the focusing direction and the tracking direction, is needed for the objective lens drive apparatus. In the objective lens drive apparatus with the multi-axial direction driving mechanism, the support rigidity will be made small so that it may be easy to carry out movement at least in a desired driving direction. This will easily affect the driving of the objective lens drive apparatus in the other directions.
For this reason, the cross talk generated between the driving axes becomes large, and it will not be negligible. The main cross talk which will not be negligible is as follows: (1) the cross talk of the radial and tangential rotation directions which is generated by the focusing and tracking movement drive; (2) the cross talk of the tracking movement direction which is generated by the radial movement drive; (3) the cross talk of the tangential rotation direction which is generated by the focusing movement drive; (4) the cross talk of the tangential movement direction which is generated by the focusing and tracking movement drive; and (5) the cross talk of the tangential movement direction which is generated by the tangential rotation drive.
Japanese Laid-Open Patent Application No. 10-275354discloses the objective lens drive apparatus which is configured to reduce the cross talk. FIG. 34 shows such a conventional objective lens drive apparatus.
As shown in FIG. 34, a pair of support members 101 and 102 which have the same structure are arranged on the plane 105 which is perpendicular to the optical axis of the objective lens 104. The ends 101a and 102a of the support members 101 and 102 are fixed to the side surfaces of the lens holder 106, respectively. The other ends 101b and 102b of the support members 101 and 102 are fixed to the stationary portion 107.
The support member 101 is composed of the first rod-like member 108 extending from the stationary portion 107 and the second rod-like member 110 extending from the lens holder 106 and being at right angles the end of the first rod-like member 108. The support member 102 is composed of the first rod-like member 109 extending from the lens holder 106 and the second rod-like member 111 extending from the lens holder 106 and being at right angles to the end of the first rod-like member 109.
The rigidity of the objective lens 104 in the tangential rotation direction is set such that the rigidity on the side of the ends 101a, 102a of the support members 101, 102 is smaller than the rigidity on the side of the other ends 101b, 102b of the support members 101, 102.
The drive magnets 112 and 113 are fixed to the lens holder 106. The drive coils 114 and 115 (the focusing coil, the tracking coil, the radial drive coil and the tangential drive coil) are provided on the stationary portion 107. By supplying electric current to the drive colis 114 and 115 respectively, the lens holder 106 including the objective lens 104 is driven in the four axial directions.
With such composition of the conventional objective lens drive apparatus, it is possible to form the movable portion into a thin structure and it is possible to provide the design in which the objective-lens principal point, the center of inertia of the movable portion and are made to be in proximity. It is possible for the conventional objective lens drive apparatus to reduce the cross talk of the tangential rotation direction which is generated when driving the lens holder 106 in the focusing direction.
However, in the conventional technique of Japanese Laid-Open Patent Application No. 10-275354, it is difficult to manage the rotation rigidity in the tangential tilt direction of the attachment section of the rod-like members 108,109 on the side of the lens holder 106 with the composition of the conventional objective lens drive apparatus of FIG. 34.
Furthermore, the lens holder is supported with the rod-like members 108 and 109. When it is configured by using the moving coil method, the wiring of the current to the lens holder 106 will run short. The conventional objective lens drive apparatus of FIG. 34 is applicable only by using the moving magnet method.
The mass of the movable portion increases when the moving magnet method is used since the magnet is provided on the side of the movable portion including the lens holder 106. The acceleration sensibility becomes small, and it is difficult to follow the optical disk which is rotated at high speed.
When the moving coil method is used, the density of the magnetic fluxs passing through the coil can be increased by enlarging the magnet in order to make sensibility increase. However, when the moving magnet method is used, it is difficult to make sensibility increase since the mass of the movable portion increases when the magnet is enlarged. It is difficult to ensure adequate level of the acceleration which can follow the surface inclination or eccentricity of the optical disk.
With the composition of the conventional objective lens drive apparatus of Japanese Laid-Open Patent Application No. 10-275354, the movable portion is configured into a thin structure, and the magnitude of the mechanical components cannot be secured enough and there is the problem that the output acceleration is low.
Structurally, the focusing operation and the tangential tilt operation tend to influence mutually, and the occurrence of the tangential tilt is caused by the focusing operation. There is also the problem that the servo control becomes unstable.
Japanese Patent No. 3029616 discloses another objective lens drive apparatus. FIG. 35 shows the composition of the main part of the conventional objective lens drive apparatus of Japanese Patent No. 3029616.
In the composition of FIG. 35, the movable portion 122 containing the objective lens 121 is supported by the ends of the four rod-like elastic support members 123–126 (two pieces on one side) which are substantially in parallel. By using the electromagnetic drive unit (not shown), the objective lens 121 can be driven in the focusing direction, the tracking direction, the radial tilt direction and the tangential tilt direction as indicated by the arrows P1 and P2 in FIG. 35.
The other ends of the rod-like elastic support members 123–126 are independently fixed to the elastic arm 129. The elastic arm 129 is provided so that it is rotatable around one of the axis 127 and the axis 128, which are parallel to the tracking direction, in the directions indicated by the arrows M1 and M2 in FIG. 35.
With the composition of FIG. 35, it is possible for the objective lens drive apparatus of Japanese Patent No. 3029616 to reduce the cross talk of the tangential tilt direction generated when the movable portion 122 is driven in the focusing direction.
However, in the conventional objective lens drive apparatus of FIG. 35, the composition of movable parts 129 and 130 on the side of the stationary portion are complicated, and the elastic properties are not stabilized. Similar to the composition of FIG. 34, in order to deal with the tilt compensation, the four rod-like elastic support members 123–126 are needed, and the wiring of current supply will run short. Hence, the composition of FIG. 35 is applicable only by using the moving magnet method. There is the problem that is the same as that of the composition of FIG. 34.
In addition, Japanese Utility Model No. 2579715 and Japanese Laid-Open Patent Application No. 6-162540 disclose the objective lens drive apparatus in which the movable portion containing the objective lens is supported by the plurality of rod-like elastic-support members. With such composition, the movability and the stability of the support are improved.
However, in the composition of Japanese Utility Model No. 2579715 or Japanese Laid-Open Patent Application No. 6-162540, when the movable portion containing the objective lens is diren in one direction, the movement of the objective lens in the other directions becomes unstable or the movement is impossible.
Moreover, Japanese Published Utility Model Application No. 5-4096 and Japanese Laid-Open Patent Application No. 11-316963 disclose the objective lens drive apparatus in which the end of the rod-like elastic support member on the side of the stationary portion is fixed to the reaf spring member.
In the composition of Japanese Published Utility Model Application No. 5-4096 or Japanese Laid-Open Patent Application No. 11-316963, the direction in which the objective lens can stably be driven is restricted to a specific direction, and the position of the light spot on the optical disk is changed when the objective lens is driven in the direction.